Photo transistors may be used for the detection of light or light signals. Silicon On Insulator (SOI) technologies utilize very small layers to form metal oxide semiconductor transistors in a complementary switching scheme to build digital CMOS circuitry. The use of optical interconnects becomes more and more interesting as the integration density increases and the required bandwidth can no longer be provided by the electrical solutions.
In order for a photo transistor to function properly, the light incident on the photo transistor must have a sufficiently large intensity to generate the specific charge density (charge/volume) needed to switch the transistor.